The invention relates generally to a roller and more particularly to a roller for compressing webs of material.
Such a roller is known from DE-A-29 07 761. There, the sealing members move out during operation and displace the hollow roller relative to the crosshead, until a force equilibrium is achieved. The position which results in this case is indefinite.
However, there is a need for positioning of the sealing members, i.e. of the hollow roller relative to the crosshead, in many cases, for example if a roller is supposed to work in a calander, with a hollow roller freely movable in the plane of effect, radially relative to the crosshead, as the bottom roller. Without positioning, the position of the hollow roller would be dependent only on the forces, and in an extreme case, the bent crosshead could come to rest on the inside circumference of the rotating hollow roller.
Therefore, controls have already been developed for positioning of the hollow rollers which are freely movable in the plane of effect, which act on support elements comparable to the sealing members (DE-B-28 49 253, DE-A-30 26 865), or on external force members which engage on the crosshead (DE-A-29 43 644). In these embodiments, however, the detour of an external regulation is taken, which is connected with a correspondingly reduced response sensitivity and significant additional expenditure.
The reference DE-C-38 05 323 indicates a direct influence on the extension movement, effective by the structure of the individual sealing member. However, this involves a sealing member of a different type, namely a support element with a throttled passage from the cylinder chamber to the bearing pocket. When the extension is too great, the sealing member releases deflection channels, which causes the pressure to collapse. The known support element therefore only serves for the purpose that in an emergency, a limit position is not exceeded from one side. This embodiment is not suitable for positioning purposes, i.e. for maintaining a certain position. This is also true because the pressure is changed when the position influence occurs, which is not allowed to happen for positioning during operation.
The invention is based on the task of allowing positioning of the hollow roller relative to the crosshead, in the plane of effect, in a direct way and without significant additional expenditure.